ATMOSPHERIC DISPERSION MODELS OF A RADIOLOGICAL DISPERSAL DEVICE OR A “DIRTY BOMB”

A Dispersal Device (RDD), according to the Department of Defense (DOD), is defined as a device, weapon or equipment, other than a nuclear weapon, specifically designed to spread radioactive materials to cause destruction, damage, or injury by means of the contamination produced from the dispersion of such materials. There are various ways and options to spread radioactive materials into the environment and cause public panic. An aerosol generator could be used to pollute air in the ventilating system of an office building or radioactive substances could be introduced into drinking water supply reservoir causing severe impact on community life. For a terrorist group, probably the easiest way to mount an RDD attack is to spread radiological contamination with conventional explosives or a pyrotechnical device. This case is commonly referred to as a “dirty bomb” and represents a subset of the general class of RDDs. To facilitate emergency preparedness and decision making in situations of threats related to radiological releases into the atmosphere (as a result of an RDD explosion) requires development of mathematical models for prediction of radiation situation at an early phase of the accident. The crucial part of the mathematical models used for environmental transport and estimation of dose and risk involved in the incident is the module for calculation of the plume dispersion. A large number of transport models have been developed that differ in the scope of processes taken into consideration and the way of accounting for their impact. Several atmospheric dispersion models for RDDs will be discussed and a general guidance for application suitability will be discussed. Emphasis will be given to Hazard Prediction and Assessment Capability (HPAC) software developed and distributed by Defense Threat Reduction Agency (DTRA). Models to fully describe the consequences of a domestic nuclear explosion (DNE) will be discussed. This work was supported by the U.S. Department of Energy, National Nuclear Security Administration Nevada Site Office, under Contract No. DE-AC08-96NV11718. DOE/NV/11718—869-ABS.